1. Field of the Invention
The present invention relates to a semiconductor device and a manufacturing method thereof. In particular, the invention relates to a method for forming an interlayer insulating film over a semiconductor element (device) such as a thin film transistor (hereinafter abbreviated as “TFT” in this specification).
2. Description of the Related Art
In a semiconductor process, an insulating film is utilized in various applications. Examples thereof are as follows: a base film for preventing an impurity such as sodium contained in a glass substrate from diffusing into a semiconductor layer of a TFT, a gate insulating film of a TFT, an interlayer insulating film for insulating and separating wirings from one another, a passivation film for protecting a surface, a capacitor insulating film of a memory cell, and the like.
In recent years, miniaturization and multi-layering of an element or a wiring have been required in order to realize higher integration and miniaturization of a semiconductor integrated circuit. An interlayer insulating film is provided to insulate wirings from each other. When a wiring, an electrode, or the like is further formed over the interlayer insulating film, the surface of the interlayer insulating film needs to be planar.
As the insulating film having planarity, an SOG film is known (for example, Reference 1: Japanese Patent Application Laid-Open No. 10-242277).
The SOG film refers to an insulating film formed by applying and then heat-treating (baking) a solution in which a silicon compound is diluted with a solvent. The SOG film is roughly divided into two types: an organic SOG film which contains an organic component in a silicon compound and an inorganic SOG film which does not contain an organic component in a silicon compound.
A resin containing a siloxane polymer can be given as an example of the SOG film. An insulating film obtained by baking the resin containing a siloxane polymer has a characteristic of having higher heat resistance than that obtained by baking a resin not containing a siloxane polymer.
The baking after applying the resin containing a siloxane polymer is conventionally performed in the atmosphere. At this time, there is a problem in that a crack is generated in the formed insulating film. In particular, the crack generation is notable in a region where the insulating film has a thickness of 1 μm or more. Note that the atmosphere means an atmosphere including nitrogen of approximately 78.1% (volume ratio) and oxygen of approximately 20.9% at room temperature (at approximately 15° C. in terms of the global mean temperature).
In order to prevent this crack generation, methods can be considered such as setting the thickness of the insulating film at 1 μm or less and adjusting resin components. However, using these methods, there are problems of poor insulation due to thin thickness of the insulating film or uneven application due to the change in resin components.